Invertebrates - 'The Velvet Worm', The Strongest Worm on The Planet

Q: When is a worm not a worm?
A: When it's a peripatus!

Usually called the Velvet Worm because of its soft texture, the Velvet Worm is not really a worm. It is possibly one of the strangest animals around although it is a very attractive little creature. Most species are no more than 4 cm (1.6 inches) long but a few do reach over 10 cm (4 inches). They are found in shades of blue, purple, brown or grey and they have 14 or more pairs of little stumpy, unjointed legs. They live strictly in moist environments and are found under rotting logs, leaf litter or soil.

A more appropriate name is the peripatus (pronounced purr - RIP - ah-tuss) but you might also see many technical publications refer to these unique invertebrates as onychophorans. The peripatus is quite ancient and fossils have been found dating back to the days when the earliest animals colonised the land (the Cambrian period, 500 million years ago). Australia has more peripatus species (48 to be exact) than anywhere else but they are Gondawanan in origin so you could also find them in Africa, South America and Southeast Asia.

The peripatus has a most unusual life cycle and is actually a voracious, nocturnal predator. Two antennae protrude from the head and these can squirt a white, sticky fluid. This happens as a defence mechanism when the little crawlers are handled but it is also used to ensnare their dinner. Once tangled up in the sticky threads, the small arthropods and invertebrates they eat are immobilised and ready to feast on. The peripatus bites a single hole into the victim through which the soft insides are sucked out. The predator's saliva assists the pre-digestion of the meal, making it easier to remove - not unlike some venomous snakes whose toxin starts to liquefy the tissues of the victim before it has been swallowed.

Even though the various species of peripatus look alike on the outside, they have some very different ways of reproducing themselves. Some lay shelled eggs while others produce live young which have been nourished by an attachment similar to a placenta. Such 'advanced' reproduction is most unusual for an animal whose first appearance in the evolution of animals was at the very beginning of the timeline.

The transfer of the male's sperm is also rather strange: some species have a small pit on their heads and the male will transfer sperm to this pit which then makes contact with the female's genitalia. There's an African species which simply leaves a 'packet' of sperm on the body of the female. The packet dissolves and the sperm are absorbed through the skin - once inside the body, they swim to the ovary where fertilisation takes place.

Peripatus are fairly common in the rainforests of the Wet Tropics but they are very hard to find - your only guaranteed look will be in a book!